Method of operating a vacuum degasser to equalize erosion of refractory leg liners

ABSTRACT

A detachable end tube for the up-leg of a vacuum degassing unit having a plurality of supply ports entering adjacent the point of attachment of the end tube and terminating in the interior channel of the tube at a point remote from the point of attachment and remote from the lower end of the tube. A method of equalizing the erosion rate of the nondetachable sections of the up-leg and down-leg of a degasser is provided which comprises removing the detachable end tube from the up-leg, attaching it to the down-leg whereby the down-leg functions as the up-leg and vice versa, and repeating said steps at approximately equal time intervals.

United States Patent 72] Inventor David E. Todd Butler, Pa. [21 1 Appl. No. 790,795 [22] Filed Jan. 13, 1969 [45] Patented Sept. 21, I971 [73] Assignee Armco Steel Corporation Middletown, Ohio [54] METHOD OF OPERATING A VACUUM DEGASSER TO EQUALIZE EROSION 0F REFRACTORY LEG LINERS 2 Claims, 2 Drawing Figs.

[5 2] 0.5. Ci. 75/49, 75/6 i 266/35, 266/38 [51] lnt.Cl C2lc 7/10 [50] Field of Search 75/49; 266/34, 35, 38

[56] References Cited UNITED STATES PATENTS .PQYEE? 3,136,834 6/1964 Lorenz 75/49 X 3,479,022 I 1/1969 Coupette 75/49 X 3,071,362 1/1963 Lorenz 75/49 X Primary Examiner-L. Dewayne Rutledge Assistant Examiner-J. Davis Attorney-Melville, Strasser, Foster & Hofiman ABSTRACT: A detachable end tube for the up-leg of a vacuum degassing unit having a plurality of supply ports entering adjacent the point of attachment of the end tube and terminating in the interior channel of the tube at a point remote from the point of attachment and remote from the lower end of the tube. A method of equalizing the erosion rate of the nondetachabie sections of the up-leg and down-leg of a degasser is provided which comprises removing the detachable end tube from the up-ieg, attaching it to the down-leg whereby the down-leg functions as the up-leg and vice versa,

1 and repeating said steps at approximately equal time intervals METHOD OF OPERATING A VACUUM DEGASSER TO EQUALIZE EROSION OF REFRACTORY LEG LINERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in apparatus for introducing inert gases into a R-H (Ruhrstahl AG.Heraeus G.m.b.I-I.) vacuum degassing unit, and particularly to the provision of a detachable end portion for the up-leg of such a unit, said end portion having gas supply ports terminating intermediate the point of attachment and the lower end thereof. The invention also provides a method for equalizing the erosion of the non detachable sections of the up-leg and down-leg by interchanging the detachable end portions at predetermined intervals, whereby the up-leg becomes the down-leg and vice versa.

2. Description of the Prior Art U.S. Pat. No. 1,921,060 issued Aug. 8, 1933, to CE. Williams, discloses the use of an injected gas to lift molten metal upwardly through a tube, followed by overflowing the metal at the top of the tube, removing gases from the molten metal by application of vacuum and returningthe molten metal to a container through another tube. This method was stated to be applicable for deoxidizing and evacuating metal by use of a reducing gas, or simply evacuating the metal by use of an inert gas.

The R-H process employs the basic teaching of the Williams patent and provides a vacuum chamber with two ceramic tubes which extend down into the molten metal. Degassing begins with an application of vacuum, drawing the stream upwardly into the vacuum chamber through both tubes. Gas, usually argon, is injected into the up-leg to effect circulation of the molten metal and to promote gas removal. The degasses stream reenters the ladle through the down-leg where its momentum and greater density carry it to the bottom of the ladle.

Multiple gas injection ports for this purpose are disclosed in U.S. Pat. No. 3,320,035, issued May 16, 1967, to A. L. Lehman. This patent further discloses periodic injections of oxygen to burn out any stoppage which may develop in the supply ports.

The design and location of the gas injection system has become a subject of great consideration due to the problem of refractory erosion and consequent need for frequent repair and replacement of the ceramic tubes. U.S. Pat. No. 3,136,834 issued to A. Lorenz discloses several ways of introducing injected gas, such as one in which the supply pipe is inserted in the molten metal so that its lower end is under or within the lower end of the up-leg. It is also suggested to extend the supply pipe concentrically downwardly within the upleg terminating near the lower end thereof.

Since the gas bubbling action takes place in the up-leg, this leg needs the most frequent repair or replacement because of severe localized erosion at and just above the point of gas injection.

In addition, accelerated erosion occurs at the ends of both legs where they contact the molten metal bath. This latter problem has led to the use of detachable refractory end portions on the legs, which are often referred to as snorkels. FIG. 3 of the above-mentioned Lorenz patent discloses such detachable snorkels which are symmetrical and hence interchangeable from the up-leg to the down-leg. In this arrangement gas is injected into the up-leg above the point of attachment of the snorkel.

U.S. Pat. No. 3,071,362, issued Jan. 1, 1963, to A. Lorenz discloses the concept of injecting the gas at the point of attachment of the snorkel joint through gas supply tubes. This patent proposed injection of gas at the snorkel joint through an annular channel and a continuous peripheral opening or a plurality of small openings.

U.S. Pat. No. 3,380,727, issued Apr. 30, 1968, to K. Ruttiger et 211. discloses the injection of gas through a downwardly directed supply pipe terminating in a refractory porous cap projecting inwardly from the inner wall of the up-leg at the lower end thereof.

Although the provision of detachable snorkels simplifies the problem of replacement due to erosion, the various means of injecting gases disclosed in the prior art do not satisfactorily solve the problems of minimizing erosion of the refractory material from which such snorkels aremade, and of easy replacement of the snorkels. For example, the Lorenz U.S. Pat. No. 3,071,362, which injects gas into the up-leg at the snorkel joint, accelerates the localized erosion problem at the point of injection. Injection of gas at or near the bottom of the snorkel results in accelerated erosion of the lower end of the snorkel. In addition, provision of a gas supply pipe within the up-leg, as in U.S. Pat. No. 3,136,834, or ofa porous cap, as in U.S. Pat. No. 3,380,727, make the removal and replacement of the snorkels difficult. Injection of gas above the snorkel joint results in erosion only of the nondetachable refractorylined section of the up-leg and accelerates the rate of erosion in this area, which is of course the most difficult and time-consuming portion of the degassing unit to repair or replace.

Moreover, detachable snorkels made wholly of refractory material are easily broken.

Finally, erosion of the refractory-lined nondetachable sections of the up-leg and down-leg proceeds at unequal rates since no gas injection occurs in the down-leg. Consequently, replacement of the refractory lining in the nondetachable section of the up-leg is required much more frequently than the down-leg and is frequently the limiting factor in operating life.

SUMMARY The present invention provides a detachable end portion or snorkel for a R-l-I vacuum degassing unit having a plurality of supply ports terminating in the interior channel of the snorkel at a point remote from the point of attachment of the snorkel to the nondetachable portion of the up-leg and remote from the lower end of the snorkel, thereby minimizing erosion of the refractory material at the'point of attachment and at the lower end of the snorkel. The detachable snorkel is easily removed and replaced due to the absence of a gas supply pipe or other supply means within the up-leg.

The invention further provides a method for equalizing erosion of the refractory-lined nondetachable sections of the upleg and down-leg by providing symmetrical snorkels which are interchangeable on the up-leg and down-leg, the snorkel for the up-leg only being provided with a plurality of gas supply ports, whereby the up-leg can function as the down-leg, and vice versa, for approximately equal periods of time simply by reversing the two snorkels and the gas supply lines connected to the snorkel having gas supply ports.

The detachable snorkel of the present invention is provided with a metallic cylindrical reinforcement member surrounded externally and internally by refractory material, thereby making it extremely durable.

BRIEF DESCRIPTION OF THE DRAWING Reference is made to the accompanying drawing wherein:

FIG. 1 is a fragmentary sectional view of a R-l-l vacuum degasser embodying the detachable snorkels of the present invention; and

FIG. 2 is a sectional view on an enlarged scale of a snorkel for the up-leg embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawing, a vacuum chamber in a R-H vacuum degasser is diagrammatically shown generally at It). The vacuum chamber is provided with an up-leg comprising a nondetachable metallic casing or shell 1 l and a refractory inner lining 12. The vacuum chamber is further provided with a nondetachable down-leg substantially identical in construction to the nondetachable up-leg, comprising a metallic casing or shell 13 and a refractory lining 14.

The up-leg is further provided with a detachable tube or snorkel indicated generally at 15, which will be described in detail hereinafter. A detachable snorkel indicated generally at 16 is also provided on the down-leg and will be described in detail hereinafter.

A vacuum connection to the chamber is indicated at 17 and may be provided with a suitable valve 18.

A refractory lined ladle for a supply of molten metal 19 is indicated at 20. As will be apparent from FIG. 1, the detachable snorkels are partially immersed in the supply of molten metal.

Upon application of vacuum the chamber 10, molten metal is drawn up both legs into the degassing chamber proper, indicated at 21, to a level determined by the height of the hearth 21a above the metal in the ladle and the degree of vacuum established in chamber 21. Injection of gas into the up-leg causes an imbalance in the system sufficient to start circulation of the molten metal as shown by arrows. In practice, it is usually desirable to keep the gas flowing continuously in order to prevent plugging and subsequent stoppage of the gas flow. The molten metal is degassed in the chamber 21 by the action of vacuum and reenters the ladle through the down-leg as indicated by arrows and tends to flow to the bottom of the ladle for reasons already indicated.

Turning to a consideration of FIG. 2, the detachable snorkel for the up-leg will be seen to include an annular metallic flange 25 from which depends a cylindrical metallic reinforcing member 26 encased within refractory inner and outer linings 27 and 28 respectively. Preferably the depending reinforcing member 26 is provided with an inwardly turned terminus 26a which will insure that the refractory lining 27 is held in place even if it should become cracked, The upper surface of the annular flange 25 is provided with a circular recess 29 in which is located an O-ring 30 of resilient material in order to insure a vacuumtight fit with a mating annular flange 31 depending from the lower extremity of the nondetachable up-leg 11.

A plurality of gas supply ports is provided in the detachable snorkel 15, each port being formed by a radial, substantially horizontal bore 32 in the annular flange 25, which communicates with a downward bore 33 passing from the flange 25 into the inner refractory lining 27 and communicating in turn with a radial substantially horizontal bore 34 in the refractory inner lining 27 which terminates in the interior channel at a point remote from the point of attachment to the nondetachable section of the up-leg and remote from the lower end of the detachable snorkel 15.

As shown diagrammatically in FIG. I, a plurality of gas supply pipes 35 is provided for connection with the horizontal bores 32 of the gas supply ports. In the exemplary embodiment of FIG. 1, four gas supply ports and four supply pipes 35 are provided. The supply pipes 35 in turn communicate with a conduit 36 which, as explained hereinafter is arranged for movement either to a point adjacent the nondetachable section 1 1, 12 or the nondetachable section 13, 14.

The degassing operation is initiated by opening the valve 18 so as to subject the degassing chamber 21 to the influence of vacuum through the line 17. Molten metal, for example steel, is drawn upwardly through both legs, and a gas, such as argon, is admitted through conduit 36 and supply lines 35 to the gas supply ports 32, 33 and 34 in the snorkel 15. The gas bubbles upwardly from the plurality of ports 34 through the molten metal in the up-leg 11, 12 and enters the chamber 21 from which it is withdrawn through vacuum line 17. As explained hereinabove, this gas injection causes circulation of the molten metal in the manner indicated by arrows in FIG. 1.

After a sufficient period of operation to result in some erosion of the refractory inner lining 12 of the nondetachable upleg, for example 25 heats, the snorkels l5 and 16 are appreciably worn; therefore the snorkel 15 is removed from the up-leg 11, 12 and the snorkel 16 is removed from the down-leg 13, 14. A new snorkel 15 is thenattached to down-leg 13, 14

and the conduit 36 and supply pipes 35 are moved sufficiently to be reconnected to the gas supply ports 32-34. A new snorkel 16 is then attached to the leg 11, 12 so that the leg 13, 14 then becomes the up-leg while the leg 11, 12 becomes the down-leg. Operation is continued with this reversal of snorkels until a substantially equal erosion has occurred in the refractory inner lining 14, when an exchange of snorkels back to the original position shown in FIG. 1 may be effected.

If, after a period of operation sufficient to result in some erosion of the refractory inner lining 12 of the nondetachable up-leg 11, 12, the snorkels 15 and 16 are not excessively worn, these partially expended snorkels may simply be interchanged, with reconnection of the gas supply lines 35 as explained above, so that the leg 13, 14 functions as the up-leg while the leg 11, 12 functions as the down-leg. Thus, this method of interchanging the two types of snorkels also permits substantial equalization of erosion in the refractory inner linings 12 and 14 of the nondetachable legs.

The snorkel 16 is identical in construction to the snorkel 15, except that it is not provided with the gas supply ports 32, 33 and 34. Both snorkels are attached to the annular flanges 31 depending from the nondetachable legs 11 and 13 by bolts or other conventional means, not shown.

It should further be noted that the annular flange 25 of the snorkels 15 and 16 has an inner diameter greater than that of the refractory lining 27 so that the upper portion of the refractory lining 27 merges smoothly with the refractory linings 12 and 14 at the attachment joints, thereby providing a smooth cylindrical passage through which the stream of molten metal passes. This minimizes the localized erosion at the joint.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of equalizing the rate of erosion of refractory linings of an up-leg and a down-leg of a vacuum degassing unit resulting from the injection of gas in the up-leg to assist the upward flow of molten metal therethrough, which comprises the steps of providing detachable, interchangeable end tubes for each of said legs, the end tube for said up-leg only being provided with gas supply ports, providing gas supply means com municating with said ports, operating said vacuum degassing unit for a predetermined period of time until appreciable erosion has occurred in the refractory lining of said up-leg, interchanging the type of and tube on said up-leg with the type of end tube on said down-leg, whereby the up-leg functions as the down-leg and the down-leg functions as the up-leg, and resuming operation for a period substantially equal to said predetermined period of time.

2. The method of claim 1, including the steps of disconnecting said gas supply means prior to interchanging said types of end tubes, and thereafter reconnecting said gas supply means to said gas supply ports. 

2. The method of claim 1, including the steps of disconnecting said gas supply means prior to interchanging said types of end tubes, and thereafter reconnecting said gas supply means to said gas supply ports. 